To setup your voice mail just call your voice mail by holding down one.
And then after you set it up you can restart your iPhone and it will work.
If not call Apple at 1-800-MY-APPLE
or at&t at 611
Thank You. Nick

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3
Look at your list of current voice messages. If you have any
messages that are eligible for recovery, you'll see an item at the very
bottom called "Deleted Messages". Tap on this to access a list of your
deleted messages.

4
You should now see a list of deleted voice messages. If you
see the message that you want to recover, tap on it and choose
"Undelete".

5
Your voice message will now be sent back to the main list of
current voice mail messages.

6
Repeat steps 1-5 for "each" message you wish to recover. This
may take time!